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Banksia
Banksia is a genus of around 170 species in the plant family Proteaceae. Iconic Australian wildflower and popular garden plants, they are easily recognised by their characteristic flower spikes and fruiting "cones" and can vary from prostrate woody shrubs to trees up to 30 metres tall. They are generally found in a wide variety of landscapes; sclerophyll forest, (occasionally) rainforest, shrubland, and some more arid landscapes, though not in Australia's deserts.
Heavy producers of nectar, banksias form a vital part of the food chain in the Australian bush. They are an important food source for all sorts of nectariferous animals, including birds, bats, rats, possums and a host of invertebrates. Furthermore, they are of economic importance to Australia's nursery and cut flower industries. However these plants are threatened by a number of processes including land clearing, frequent burning and disease, and a number of species are rare and endangered.
Banksias grow as trees or woody shrubs. Trees of the largest species, B. integrifolia (Coast Banksia) and B. seminuda (River Banksia), often grow over 15 metres tall, and may be up to 30 metres tall[1]. Banksia species that grow as shrubs are usually erect, but there are several species that are prostrate, with branches that grow on or below the soil.
Flowers
Banksias are most easily recognised by their characteristic flower spike, known as an inflorescence, and the woody fruiting structures that appear after flowering. The flower spike consists of a central woody axis with a furry coating; it is generally held erect, but hangs down in a few species. This axis is covered in tightly-packed pairs of flowers, which are attached to the axis at right angles. A single flower spike generally contains hundreds, if not thousands of flowers. The most recorded is around 6000 individual flowers on inflorescences of Banksias grandis.
Banksia flowers are usually a shade of yellow, but orange, red and pink flowers also occur. The colour of the flowers is determined by the colour of the perianth parts and often the style. The style is much longer than the perianth, and is initially trapped by the upper perianth parts. These are gradually released over a period of days, either from top to bottom or from bottom to top. When the styles and perianth parts are different colours, the visual effect is of a colour change sweeping along the spike. This can be most spectacular in B. prionotes (Acorn Banksia) and related species, as the white inflorescence in bud becomes a brilliant orange. In most case, the individual flowers are tall, thin saccate (sack-shaped) in shape. Occasionally, multiple flower spikes can form. This is most often seen in Banksia marginata and Banksia ericifolia.
Taxonomy
The Banksia genus was first described and named by Carolus Linnaeus the Younger in his April 1782 publication Supplementum Plantarum; hence the full name for the genus is "Banksia L.f." The genus name honours the English botanist Sir Joseph Banks, who collected the first Banksia specimens in 1770, during James Cook's first expedition.
Banksia belongs to the family Proteaceae, subfamily Grevilleoideae, and tribe Banksieae. Banksia and the closely related Dryandra are placed together in subtribe Banksiinae, mainly because in both genera the flowers occur in condensed heads. Recent research into the relationship between Banksia and Dryandra has suggested that Dryandra should be sunk into Banksia.
Ecology
Banksias are heavy producers of nectar, and so are important sources of food for nectariferous animals, including honeyeaters and small mammals such as rodents, antechinus, honey possums, pygmy possums, gliders and bats. Many of these animals play a role in pollination of Banksia. Various studies have shown mammals and birds to be important pollinators. An interesting observation by Carpenter in 1978 was that some banksias had a stronger odour at night possibly to attract mammal pollinators. Other associated fauna include the larvae of moths (such as the Dryandra Moth) and weevils, which burrow into the "cones" to eat the seeds and pupate in the follicles; and birds such as cockatoos, who break off the "cones" to eat both the seeds and the insect larvae.
Garden
Banksias are popular garden plants in Australia because of their large, showy flower heads, and because the large amounts of nectar they produce attracts birds and small mammals. Popular garden species include B. spinulosa, B. ericifolia, B. aemula (Wallum Banksia ), B. serrata (Saw Banksia), Banksia media (Southern Plains Banksia) and the cultivar Banksia 'Giant Candles'. Banksia species are primarily propagated by seed in the home garden as cuttings can be difficult to strike. However commercial nurserymen extensively utilize the latter method (indeed, cultivars by nature must be vegetatively propagated by cuttings or grafting).
Selected species
The Southern Plains Banksia (Banksia media), also known as Golden Stalk Banksia, is a species of shrub in the plant genus Banksia. It occurs on the south coast of Western Australia between Albany and Israelite Bay, where it is a common plant.
Banksia serrata, commonly known as Old Man Banksia, Saw Banksia, Saw-tooth Banksia and Red Honeysuckle, is one of the most common species of Banksia along the east coast of Australia.
Banksia aemula, previously known in New South Wales as Banksia serratifolia, is a lignotuberous shrub closely related to Banksia serrata. In fact it derives its specific name, aemula from the latin for 'similar', due to its similarity to B. serrata. it is found from Bundaberg south down to Sydney on the Australian east coast.
Banksia blechnifolia is a species of prostrate shrub in the plant genus Banksia. Found in sandy soils in the south coastal region of Western Australia in the vicinity of Lake King, it is non-lignotuberous, regenerating by seed after bushfire. It gained its specific name as its leaves are reminiscent of fern (blechnum) leaves.
Banksia petiolaris is one of the prostrate banksias, a group with horizontal stems and thick, leathery upright leaves. Found in sandy soils in the south coastal regions of Western Australia in the vicinity of Esperance. It is nonlignotuberous, regenerating by seed after bushfire.
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